Uveitis is a major cause of blindness in the United States. Pars planitis is a well-defined disease subset of uveitis. The causes of pars planitis and of other uveitis subsets are unknown. The overall objective of this project is to characterize a distinctive protein found in circulating immune complexes (CIC) in the plasma of pars planitis patients during acute exacerbation of the disease and to investigate the possible role of this protein in the pathogenesis of pars planitis. A knowledge of the antigen and antibody molecules which form CIC in pars planitis would be a major advance toward its treatment and possible cure. The specific aims of this project are (1) to isolate the unique protein in CIC from pars planitis patients by gel electrophoresis and to characterize it by determining its partial amino acid sequence; (2) to characterize antibodies in CIC and free circulating antibodies to the unique protein with respect to their immunoglobulin isotypes. The unique protein of pars planitis will be separated from CIC by gel electrophoresis, transferred by electroblotting to polyvinylidene diffluoride membranes, and subjectived directly to microsequence analysis. The sequences obtained will be compared to those of known proteins in a computer database in order to unambiguously identify the protein. Antibodies will be dissociated from CIC by column chromatography in a dissociating solvent. Free circulating antibodies in pars planitis plasma specific for the unique protein will be identified by Western blot analysis. Both types of antibodies will be characterized serologically to identify their heavy and light chain isotypes.